As it is generally known, voicemail is an electronic system that may be used to store a message left by a caller for later retrieval by an intended call recipient. A call may be transferred to a voicemail box of a called telephone number when the call is not answered by a human after a pre-determined number of rings, and/or in response to various configuration settings and/or user actions. Voicemail messages may be stored as digitized audio, and may be retrieved from the voicemail box as audio, or translated into text for visual display. Most mobile network operators offer voicemail as a basic feature, and many corporate Private Branch Exchanges (PBXs) include internal voice-messaging services. Voicemail subscriptions are also available to land line subscribers.
When a telephone call is transferred to a voicemail box, the voicemail system locates and plays out a voicemail greeting for the voicemail box. The voicemail greeting may include customized audio content entered by the voicemail box owner, e.g. a name of the person, department or organization associated with the telephone number, or other customized content. The voicemail greeting may also include one or more default prompts that are automatically generated, e.g. that instruct the caller as to various options with regard to leaving a message, contacting an operator, etc.
In certain circumstances, it may be desirable to detect when a call has been answered by a voicemail system. For example, when an automated calling system places a call, it may be desirable for the system to perform one action in the event that the call is answered by a human, and another, different action, if the call is instead answered by a voicemail system.